A drive support apparatus for, for example, collision prediction and preventing collision between two vehicles is disclosed in a patent document, Japanese Patent Laid-Open No. 2008-97413, (Patent document 1). From such drive support apparatus, the drive support is provided for a driver of a subject vehicle having the apparatus in the following manner. That is, the subject vehicle bi-directionally communicates with other vehicle while predicting a future vehicle position for both of the subject vehicle and the other vehicle. Then, the predicted subject vehicle position and the predicted other vehicle position are compared with each other at a certain time of the future. Based on the comparison result, the possibility of collision is determined based on a closeness of the two vehicle's positions, and, when the predicted two vehicle's positions are very close to each other, safety support information is provided for the driver from the drive support apparatus.
For realizing the technique of the patent document 1, the position of the subject vehicle has to be predicted as a position on a road that is represented by map data, or by road map information. Thus, the current position of the subject vehicle has to be sequentially determined, point to point on a certain road. The current position of the subject vehicle may be determined by a well-known satellite navigation signal from a satellite of a Global Navigation Satellite System (GNSS), for example. The navigation signal from the satellite, however, includes a position determination error, which may result in an error of the determined current position, i.e., a position of the subject vehicle that is actually traveling on a certain road may sometimes be determined as a position other than, outside of, a traveling road due to the position determination error in a “GNSS current position” that is derived from the GNSS navigation signal described above.
A technique for correcting the GNSS current position is known, for example, as a map-matching. The map-matching corrects the current position of the vehicle onto a road by matching (i) a travel locus of the vehicle, which is a collection of the sequentially-determined current positions with (ii) a road shape of a road.
However, the map-matching may also be prone to a matching error, e.g., may wrongly match the travel locus of the vehicle to a road, i.e., to a road shape that is not completely matching with the travel locus, when a road shape somewhat close to the travel locus is found at a proximity of the current position, or in other words, a true/actual road on which the vehicle is traveling. Therefore, in some cases, the current position of the vehicle may be corrected, i.e., map-matched, to a different road that is different from the currently-traveling road.
Thus, the drive support based always on the map-matched current position may not yield an intended result, i.e., may lead to a situation in which the drive support is not provided when the support is actually needed.
The positioning of the subject vehicle and the other vehicle may also be performed, not by the map-matching, but by utilizing the GNSS current positions and the travel directions of those vehicles. By not performing the map-matching, lack of the drive support due to the current position wrongly matched to a different road will not be caused.
However, by not performing the map-matching, a collision possibility may be wrongly determined based on a wrong prediction of crossing of the two roads, i.e., the road traveled by the subject vehicle and the road traveled by the other vehicle which are actually not crossing with each other. Based on such a wrong prediction, an unnecessary drive support is provided for the driver.